1. Field of the Invention
The invention relates to decelerator apparatus for hot rolled product being produced in a rolling mill.
2. Description of the Prior Art
Rolled product generally leaves the finishing stand of a rolling mill at a speed roughly inversely proportional to its cross sectional area so as to maintain as near as possible a constant rolling rate in terms of tonnage of finished product produced.
When rolled product is delivered in straight lengths from the finishing stand it is cut into the lengths required and these then have to be brought to rest before being transferred sideways across a cooling bed. However, it will be understood that the smaller the cross sectional area of the rolled product, the greater is the rolling speed and consequently the greater is the stopping distance required before the lengths of product can be moved sideways onto the cooling bed. There is obviously a practical limit to the distance over which the lengths of product can be allowed to decelerate and the time this takes which has to be within the cycle time of products being delivered from the mill less time for the bed to clear the first notch of the cooling bed. The result is that in many of the higher production rolling mills it is found that the rolling rate in terms of tonnage produced per hour drops substantially when product of relatively small cross sectional area is being produced purely because of the high output speed of the product from the finishing stand.
Various attempts have been made to solve this problem. For example, so-called double lifting aprons associated with walking beam type cooling beds have been used, and have reduced the sliding time of the lengths of product on the take off apron immediately following the finishing stand and also before the first rake. In other words, the total sliding time of a length of rolled product has been shared between the two systems, but in fact the overall sliding distance has not been affected to any significant extent. A more positive action not limited by the frictional force which can be generated by the weight of the product on a supporting surface has been used, this involving the provision of so-called pinch rolls between which the lengths of product after having been sheared to length are trapped near to their back ends and, by virtue of the relatively slow running of said pinch rolls, decelerated fairly quickly. However, this has various drawbacks. For example, it is not easy to provide variable controlled deceleration when using pinch rolls because they depend ultimately on indeterminate frictional contact if deformation of the rolled product is to be minimised. Furthermore, the longer the length of rolled product and the greater its weight. Consequently, the greater is the required pressure applied to the surfaces of the product by the pinch rolls. The result is that some marking of the product is always likely to occur and in some cases the trailing end of a length of product can be deformed. In fact the hot rolled product can be pulled in two or severely necked. For this reason the use of pinch rolls is usually limited to the production of relatively short lengths of rolled product of round cross section or a cross section of some other simple shape.
A further braking device which has been used for the braking of lengths of wire which have been produced in a wire rolling mill has included a number of tiltable braking elements equipped with rollers, the device also including mechanism for tilting the tiltable braking elements by a variable amount. Such a device has been used to brake the lengths of wire, after they have been sheared to length, the braking effect being produced solely by the flexing of the wire as it passes through the device. In other words, the braking effect has been due to the deformation of the wire and by the physical work which has been put into the material by such deformation. For this reason, the amount of braking which can thereby be brought about by such a device on hot rolled lengths of material of relatively small cross sectional area is very small indeed and is very largely indeterminate.